Fix partial signatures, fixes #1371

jedi/evaluate/signature.py

@@ -1,19 +1,7 @@
 from jedi._compatibility import Parameter
 
 
-class AbstractSignature(object):
-    def __init__(self, context, is_bound=False):
-        self.context = context
-        self.is_bound = is_bound
-
-    @property
-    def name(self):
-        return self.context.name
-
-    @property
-    def annotation_string(self):
-        return ''
-
+class _SignatureMixin(object):
     def to_string(self):
         def param_strings():
             is_positional = False
@@ -42,9 +30,6 @@ class AbstractSignature(object):
             s += ' -> ' + annotation
         return s
 
-    def bind(self, context):
-        raise NotImplementedError
-
     def get_param_names(self):
         param_names = self._function_context.get_param_names()
         if self.is_bound:
@@ -52,6 +37,23 @@ class AbstractSignature(object):
         return param_names
 
 
+class AbstractSignature(_SignatureMixin):
+    def __init__(self, context, is_bound=False):
+        self.context = context
+        self.is_bound = is_bound
+
+    @property
+    def name(self):
+        return self.context.name
+
+    @property
+    def annotation_string(self):
+        return ''
+
+    def bind(self, context):
+        raise NotImplementedError
+
+
 class TreeSignature(AbstractSignature):
     def __init__(self, context, function_context=None, is_bound=False):
         super(TreeSignature, self).__init__(context, is_bound)
@@ -92,3 +94,11 @@ class BuiltinSignature(AbstractSignature):
     def bind(self, context):
         assert not self.is_bound
         return BuiltinSignature(context, self._return_string, is_bound=True)
+
+
+class SignatureWrapper(_SignatureMixin):
+    def __init__(self, wrapped_signature):
+        self._wrapped_signature = wrapped_signature
+
+    def __getattr__(self, name):
+        return getattr(self._wrapped_signature, name)

jedi/plugins/stdlib.py

@@ -32,7 +32,7 @@ from jedi.evaluate.names import ContextName, BaseTreeParamName
 from jedi.evaluate.syntax_tree import is_string
 from jedi.evaluate.filters import AttributeOverwrite, publish_method, \
     ParserTreeFilter, DictFilter
-from jedi.evaluate.signature import AbstractSignature
+from jedi.evaluate.signature import AbstractSignature, SignatureWrapper
 
 
 # Copied from Python 3.6's stdlib.
@@ -477,17 +477,49 @@ class PartialObject(object):
     def __getattr__(self, name):
         return getattr(self._actual_context, name)
 
-    def py__call__(self, arguments):
-        key, lazy_context = next(self._arguments.unpack(), (None, None))
+    def _get_function(self, unpacked_arguments):
+        key, lazy_context = next(unpacked_arguments, (None, None))
         if key is not None or lazy_context is None:
             debug.warning("Partial should have a proper function %s", self._arguments)
+            return None
+        return lazy_context.infer()
+
+    def get_signatures(self):
+        unpacked_arguments = self._arguments.unpack()
+        func = self._get_function(unpacked_arguments)
+        if func is None:
+            return []
+
+        arg_count = 0
+        keys = set()
+        for key, _ in unpacked_arguments:
+            if key is None:
+                arg_count += 1
+            else:
+                keys.add(key)
+        return [PartialSignature(s, arg_count, keys) for s in func.get_signatures()]
+
+    def py__call__(self, arguments):
+        func = self._get_function(self._arguments.unpack())
+        if func is None:
             return NO_CONTEXTS
 
-        return lazy_context.infer().execute(
+        return func.execute(
             MergedPartialArguments(self._arguments, arguments)
         )
 
 
+class PartialSignature(SignatureWrapper):
+    def __init__(self, wrapped_signature, skipped_arg_count, skipped_arg_set):
+        super(PartialSignature, self).__init__(wrapped_signature)
+        self._skipped_arg_count = skipped_arg_count
+        self._skipped_arg_set = skipped_arg_set
+
+    def get_param_names(self):
+        names = self._wrapped_signature.get_param_names()[self._skipped_arg_count:]
+        return [n for n in names if n.string_name not in self._skipped_arg_set]
+
+
 class MergedPartialArguments(AbstractArguments):
     def __init__(self, partial_arguments, call_arguments):
         self._partial_arguments = partial_arguments

test/test_evaluate/test_signature.py

@@ -47,6 +47,19 @@ class X:
         pass
 '''
 
+
+partial_code = '''
+import functools
+
+def func(a, b, c):
+    pass
+
+a = functools.partial(func)
+b = functools.partial(func, 1)
+c = functools.partial(func, 1, c=2)
+d = functools.partial()
+'''
+
 @pytest.mark.parametrize(
     'code, expected', [
         ('def f(a, * args, x): pass\n f(', 'f(a, *args, x)'),
@@ -59,6 +72,11 @@ class X:
         (classmethod_code + 'X().x(', 'x(cls, a, b)'),
         (classmethod_code + 'X.static(', 'static(a, b)'),
         (classmethod_code + 'X().static(', 'static(a, b)'),
+
+        (partial_code + 'a(', 'func(a, b, c)'),
+        (partial_code + 'b(', 'func(b, c)'),
+        (partial_code + 'c(', 'func(b)'),
+        (partial_code + 'd(', None),
     ]
 )
 def test_tree_signature(Script, environment, code, expected):
@@ -66,6 +84,9 @@ def test_tree_signature(Script, environment, code, expected):
     if environment.version_info < (3, 8):
         pytest.skip()
 
+    if expected is None:
+        assert not Script(code).call_signatures()
+    else:
         sig, = Script(code).call_signatures()
         assert expected == sig._signature.to_string()